Acid pickling inhibitor



252. cowosmows,

Patented May 18, 1937 UNITED STATES PATENT OFFICE ACID PICKLING INHIBITOR No Drawing.

10 Claims.

The present invention relates to the protection of iron and steel from corrosion in the presence of acids; and more particularly it concerns a corrosion inhibitor and a method for its employment in the general type of operations requiring the use of acidic materials in contact with iron and steel. The invention has especial utility in the usual pickling operations in iron and steel mills wherein the ferrous metal or alloy is treated with a dilute mineral acid to remove oxide scale, rust, and other deposits from steel billets, sheets, tubes, and rods.

In these pickling operations the dilute acid not only cleans the surface of the metal of oxide impurities, but, unless there is present some agency to prevent such action, the acid attacks the metal itself, causing loss of metal; and the hydrogen thus evolved occludes acid and distributes this corrosive liquid upon all equipment in the vicinity.

The present invention is based upon the discovery that this objectionable feature of the pickling process may be greatly minimized if there is added to the pickling liquor or bath a small amount of a nitrogen-substituted parazine or parazine derivative, which serves to restrain the acid of the acid material from attacking the oxide-free metal but without undesirably retarding its primary oxide-removing action.

According to the invention a small amount of the selected parazine derivative is added to the acid pickling solution, and this solution is then used under conditions duplicating in so far as is possible the conditions encountered in mill practice with respect to the acid concentrations and temperatures used.

The arazine derivatives employed in the present inventmn include individual compounds, as well as more or less complex mixtures thereof, generally of high molecular weight, with or without other compounds which may exert a definite corrosion-inhibiting action, such as those hereinafter named. The parazine derivatives are compounds having a saturated six-membered Application November 15, 1934, Serial No. 753,121

Inhibitor compositions of the present invention include certain reaction mixtures containing high-boiling amines of complex structure. In the manufacture of ethylene diamine by reacting ethylene dichloride with an excess of aqueous ammonia at elevated temperatures, generally around -90 C., evaporating the reaction product to remove excess reactants, and treating the residual mixture with caustic alkali, there are produced a series of polyethylene polyamines, consisting of both the piperazine and straightchain types. While the lower members such as ethylene diamine, piperazine, and triethylene tetramine possess relatively little inhibiting action, the residue of amines, particularly that portion boiling above tetraethylene pentamine, that is to say, above about 300 C. are very efiective corrosion inhibitors. Such residues evidently are complex mixtures of polyethylene polyamines which contain in large part molecules having at least one piperazine grouping.

If desired, the corrosion-inhibiting efiectiveness of this product or residue may be enhanced greatly by reacting the same under reflux with additional ethylene dichloride. The molecular size thus is increased both by linking of molecules,

and by piperazine formation wherein R R, R and R may represent hydro-' gen or the same or different alkyl, aryl, aralkyl or substituted alkyl groups.

The final product is a viscous mass which swells in water, and is soluble in an excess of water. It apparently is a hydrochloride of a polyamine. Upon treatment of this hydrochloride with strong caustic alkali solution, the corresponding insoluble base is prepared, having physical properties similar to the hydrochloride. excellent corrosion inhibitors.

Another important source of the parazine derivative are the reaction mixtures resulting from the treatment of the dichlorethyl ether with an excess of aqueous ammonia. in the manufacture of morpholine. The final products of this reaction include morpholine, morpoline ethanol, vinoxy ethyl morpholine, and still higher boiling amines. These morpholine derivatives are excellent pickling inhibitors, either alone or in the form of the crude mixture. Mixtures of these products boiling above morpholine ethanol, 1. e. those boiling around 230 C. or above, serve efiectively for the purpose.

Furthermore, by treatment of the ammoniadichlorethyl ether reaction product with an excess of caustic alkali, distilling off the volatile amines, separating from the caustic alkali by gravity or by extraction the resultant supernatant layer of amine compounds insoluble in the caustic, and distilling this material to remove morpholine, morpholine ethanol, and vinoxy ethyl morpholine, a residue of high-boiling amines remains, which not only is an excellent corrosion inhibitor, but retains its inhibiting power when present in the acid pickling liquor in very low concentrations, as indicated in the table. (Composition A.)

The following examples serve to illustrate the practice of the invention. In making the tests recorded in the table, specimens of clean, oxidefree steel of nearly identical weight and area (2.6 sq. cm.) were immersed in a 4% aqueous solution of sulphuric acid containing a known weight of the inhibitor to be tested, and were maintained at a constant temperature of 71 C. for definite periods of time. The hydrogen thereby evolved was measured, and the volume of hydrogen was taken as an indication of the degree to which the action of the acid upon the steel as retarded by the inhibitor employed. The amine percentages set out in the table are based upon the weight of 66 B. sulphuric acid used.

These bases are TABLE Pickling liquor 4% aqueous solution of sulphuric acid Temperature 71 C. Area of sample 2.6 sq. cm.

Vol. of H evolved in Perin ccs in Amine cent amine 10 min. 25 Blim 38. 4 (Eva) Morpholine ethanol 25* 17.6 Thlomorpholine ethanol hydrochloride 25 1. 0 2. 4 Thiomorpholine ethanol hydrochloride 2- 5 7. 5 19.0 Thiomorpholine ethanol hydrochloride 1. 0 10. 4 27. 0 Phenyl morpholine--..- 25 14.4 40. 5 Dimethyl morpholine isopropanoL. 25 15. 7 38. 8 Dimorpholim'um chloride............ 25 6. 8 16. 1 Dimorpholinium chloride 2. 5 l7. 0 B. 2 Diphenyl piperazine.-. 25 5. 7 l3. 4 Diphenyl piperazine--- 2. 5 11. 1 28. 4 a. it .2-3 Composition A 0 3 0 I .25 9.7 24.2 Composition 3.5 183% 2. 5 6. 0 14. 2 Composition C 1.0 6. 6 16.0 25 13. 6 3L 2 Composition D 2.6 11.2 27.4

Referring now to the table, Composition A is the high-boiling morpholine distillation residue containing parazine derivatives formed as a byproduct in the manufacture of morpholine by reacting together fifi dichlorethyl ether and aqueous ammonia, as described above.

Composition B is a fraction of the high-boiling amine residues containing parazine derivatives, and formed in the manufacture of ethylene diamine by reacting ethylene dichloride and aqueous ammonia, the said fraction boiling above 300 C. at atmospheric pressure.

Composition C is a product of higher molecular weight than composition B, and was produced by treating upon a steam bath under reflux parts by weight of the high boiling ethylene amine residues formed in the reaction of ammonia and ethylene dichloride with 70 parts by weight of ethylene dichloride, added in small portions. The final product, after dilution with water, was a viscous mass which swelled in water, and was soluble in an excess thereof.

Composition D is a viscous, water-soluble liquid having a molecular weight about 40% above that of Composition B, and produced by reacting Composition B, containing the polyethylene amine residues, with diethyl sulphate under reflux.

Compositions found to be valuable corrosion inhibitors also may be produced by reacting the ethylene amine residues (Composition B) with ethylene dichloride, under reflux over a strong caustic soda solution, the amine hydrochlorides first formed being converted back continuously to free bases which then react further. The product is a solid mass which, after washing with caustic soda, hot water, and methanol, and drying, consists of resinous, hard, tough granules, insoluble in water and in organic solvents, and slightly soluble in dilute sulphuric acid. Its properties suggest a predominantly piperazine structure with probable cross-linkage of the polyethylene amine chains.

Morpholine ethanol may be obtained from the reaction mixture produced by reacting ammonia and 5,3 dichlorethyl ether in morpholine manufacture. It boils at 225 C. at atmospheric pressure. Its formula may be written as follows:

CHgCH:

O NCHzCHzOH onion,

Diphenyl piperazine is formed by reacting aniline with ethylene dichloride, and treating the reaction mixture with aqueous caustic alkali. It is a solid at ordinary temperatures, having the structure CHaCHl OoHs-N\ "04m Omen, Dimorpholinium chloride o/OHr-OE CHrCH: J1 CH1CH2 may be formed by slowly adding one-half mol. of pp'dichlorethyl ether to a mol. of morpholine while heating the mixture under reflux, and the dimorpholinium chloride is recovered from the mixture after fractional crystallization of the morpholine hydrochloride concurrently formed. The corresponding other halides may be made similarly by use of the appropriate dihalogenated diethyl ether.

The important action of the parazine grouping in the corrosion inhibiting compositions of the present invention seems to be emphasized by the 252. COMPOSITIONS,

fact that morpholine ethanol is twice as eflective a corrosion inhibitor as is triethanolamine; and diphenyl piperazine is twice as eflective as diphenyl ethylene diamine.

While sulphuric acid is the only acid specifically mentioned in the foregoing examples, these inhibitors also are eiiective with hydrochloric acid, and the other acids suitable for use in the pickling of iron and steel.

Very small quantities, less than 1% of these compounds based on the acid bath, are efiective for the purpose indicated. It will be understood that by properly selecting the inhibitor and adjusting the amount thereof employed, almost any desired degree of corrosion inhibition may be secured.

The inhibitors may be used in the presence of foaming agents, or of other compounds sometimes present in the pickling liquor to facilitate scale removal or for other purposes.

We claim:

1. A pickling bath for iron and steel products, which comprises an acid solution containing a small proportion of a parazine derivative having in the para position to the nitrogen an atom selected from the group consisting of nitrogen and sulphur.

2. An acid pickling bath adapted for the treatment of iron and steel, said bath having incorporated therein a small proportion of a mixture of high-boiling polyethylene polyamines boiling at not substantially less than 300 C. at atmospheric pressure, the said mixture being identical with that formed by reacting ethylene dichloride and aqueous ammonia, and treating the resultant reaction mixture with a strong alkali.

3. In the process of preventing corrosion of iron and steel products by a solution of an acidic substance, the step consisting in adding to the said solution as a corrosion inhibitor a small proportion of a parazine derivative having in the para position to the nitrogen an atom selected from the group consisting of nitrogen and sulphur.

4. In the process of preventing corrosion of iron and steel products by a solution of an acidic substance, the step consisting in adding to the said solution as a corrosion inhibitor a small proportion of the mixture of polyethylene polyamines, boiling at temperatures at least as high ixamiii as around 300 C. at atmospheric pressure, and formed by reacting ethylene dichloride with aqueous ammonia, and treating the resultant reaction mixture with an alkali.

5. An acid pickling bath adapted for the treatment of iron and steel, said bath having incorporated therein a small proportion of a highboiling amine residue containing at least one parazine derivative.

6. An acid pickling bath adapted for the treatment of iron and steel, said bath having incorporated therein a small proportion of a highboiling polyethylene amine residue boiling above about 300 C. at atmospheric pressure and containing at least one parazine derivative.

'7. An acid pickling bath adapted for the treatment of iron and steel, said bath having incorporated therein a small proportion of a mixture of high-boiling polyethylene polyamines formed by reacting an ethylene dihalide with the highboiling amine residue produced upon reacting ammonia and ethylene dichloride and treating the resultant reaction mixture with a strong alkali.

8. In the process of preventing corrosion of iron and steel products by a solution of an acidic substance, the step consisting in adding to the said solution as a corrosion inhibitor a small proportion of a high-boiling amine residue containing at least one parazine derivative.

9. In the process of preventing corrosion of iron and steel products by a solution of an acidic substance, the step consisting in adding to the said solution as a corrosion inhibitor a small proportion of a high-boiling polyethylene amine residue boiling above 230 C. at atmospheric pressure, and containing at least one parazine deriv- 

